ws.js

createFrame(data) {
  const payload = JSON.stringify(data);

  const payloadByteLength = Buffer.byteLength(payload);
  let payloadBytesOffset = 2;
  let payloadLength = payloadByteLength;

  if (payloadByteLength > 65535) { // length value cannot fit in 2 bytes
    payloadBytesOffset += 8;
    payloadLength = 127;
  } else if (payloadByteLength > 125) {
    payloadBytesOffset += 2;
    payloadLength = 126;
  }

  const buffer = Buffer.alloc(payloadBytesOffset + payloadByteLength);

  // first byte
  buffer.writeUInt8(0b10000001, 0); // [FIN (1), RSV1 (0), RSV2 (0), RSV3 (0), Opсode (0x01 - text frame)]

  buffer[1] = payloadLength; // second byte - actual payload size (if <= 125 bytes) or 126, or 127

  if (payloadLength === 126) { // write actual payload length as a 16-bit unsigned integer
    buffer.writeUInt16BE(payloadByteLength, 2);
  } else if (payloadByteLength === 127) { // write actual payload length as a 64-bit unsigned integer
    buffer.writeBigUInt64BE(BigInt(payloadByteLength), 2);
  }

  buffer.write(payload, payloadBytesOffset);
  return buffer;
}